Pallet truck with hydraulic lift

ABSTRACT

A pallet truck hydraulic jack has a base plate mounting a lift cylinder with a reciprocal piston or lift rod and a pump cylinder with a reciprocal pump piston. A frame mounts a pair of forks having retractable rollers at their ends and is pivotally mounted upon the base plate and operatively engaged by the lift rod for raising the frame and lowering the rollers. A hydraulic reservoir is mounted upon the base plate. A hydraulic control system includes a pivot axle depending from the base plate having a bore coaxial of the lift cylinder. A plunger piston within the axle shaft bore is connected to the lift cylinder piston rod. There are a plurality of manifold passages formed in the base plate, adapted for supplying pressurized hydraulic fluid from the pump to the plunger piston and to the lift rod, which interconnects the reservoir and the pump and interconnects the reservoir and the lift cylinder. A cartridge type directional control valve assembly within the base plate controls the flow of pressurized hydraulic fluid in the respective manifold passages so that manual actuation of the pump effects a quick lift of the frame when it is unloaded, effects an additional application of lifting force through the lift cylinder when the frame is loaded, bypasses pressurized hydraulic fluid to the reservoir when the frame is overloaded, and provides a release of pressurized hydraulic fluid from the pump cylinder and the lift plunger and returns it to the reservoir for lowering the frame and forks. The cartridge type directional control valve may be conveniently removed and replaced in the hydraulic control circuit when required in minimum time.

RELATED APPLICATION

The hydraulically operated pallet lift truck described herein may beprovided with a mechanical emergency brake as disclosed and claimed inapplicant's copending U.S. patent application entitled "Brake Assemblyfor Pallet Lift Truck", Ser. No. 296,103 , filed Aug. 26. 1981 now U.S.Pat. No. 4,424,885, issued Jan. 10, 1984.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Pallet trucks with hydraulic lift are used in industry for lifting andtransporting loaded pallets and for unloading same at various locations.

2. Description of the Prior Art

The pallet truck includes a hydraulic jack supporting a frame carrying apair of forwardly extending forks or a platform. Specifically itincludes a lift cylinder supporting the frame and the connected forks orplatform and a pump cylinder for providing pressurized hydraulic fluidto the lift cylinder. One commercial device which I invented isillustrated and described in the Israel patent application No. 55,148published in Israel on Feb. 27, 1981. The application is entitled "DualRate Jack System For Lift Trucks" and is owned by Koor Metal, Ltd. Thepallet truck hydraulic lift described therein employs a hydraulic jackof the type wherein the handle for the pallet truck is pivotally mountedupon the lift cylinder or base and is provided with a connection withthe pump cylinder or pump piston so that pivotal movements of the handleactuates the pump cylinder. The forks of the pallet truck at theirforward ends have retractable support rollers which are operated bysuitable linkage. Upon activation of the lift cylinder raising theframe, the linkage lowers the rollers pivotally with respect to theforks. Such activation lifts the forks into engagement with the undersurface of a loaded pallet. Further pumping action of the handleelevates the frame and forks thereby lifting the pallet off of theground surface for transporting it to another location.

Other pallet truck hydraulic jack assemblies and related prior art liftdevices are shown in the following U.S. patents:

    ______________________________________                                        2,049,335     7-28-36      Stephens                                           2,309,138     1-26-43      Quayle                                             2,461,212     2-8-49       Hanna                                              3,462,167     8-19-69      Rateau                                             2,488,521     11-22-49     Barrett                                            2,993,703     7-25-61      Paradise                                           3,118,107     6-8-65       Quale                                              3,119,627     1-28-64      Klumb                                              3,286,985     11-22-49     Barrett                                            2,993,703     7-25-61      Paradise                                           3,118,107     6-8-65       Quale                                              3,119,627     1-28-64      Klumb                                              3,286,985     11-22-66     Edera                                              3,567,240     3-2-71       Brassington                                        3,608,922     9-28-71      Best et al                                         3,701,211     10-31-72     Best                                               3,757,523     9-11-73      Resuggan                                           3,775,027     11-27-73     Craft                                              3,817,546     6-18-74      Suguira                                            3,843,147     10-22-74     Fredricson                                         3,940,338     2-24-76      Btyntse, et al                                     ______________________________________                                    

It is well known that a hydraulic pallet truck for lifting andtransporting of pallets and heavy loads having the following basicelements: a hydraulic jack, a frame, steering wheels, and load rollers.The hydraulic jack is comprised of a handle operated pump mounted on abase plate under which is mounted a vertical pivot axle for thearticulated steering wheels, and two concentric cylinders with dualdiameter and a dual rate lifting piston. Such are described in theaforementioned Israeli patent application.

SUMMARY OF THE PRESENT INVENTION

The present invention relates primarily to a pallet truck with hydrauliclift which significantly reduces operational efforts, by utilizing amanually lever operated pump to provide the mechanical advantage for thehydraulic lifting of the platform or the forks of the pallet lift truckin two different lifting ratios per pump stroke. The first ratio is arapid-lift with no load. At such time the hydraulic lift device requiresonly a single stroke of the pump to raise the platform or forks of thepallet truck to engage the load. The second ratio occurs at normal liftunder load. At such time the hydraulic control system or hydraulic liftraises the forks or platform of the pallet truck by decreasing the liftratio and increasing the mechanical advantage. This feature has certaineconomical advantages in that it saves time and labor by allowing orpermitting the operator to raise any height pallet with a maximum ofthree pump strokes.

The present invention provides for the interaction of three basicelements of a hydraulic lifting unit or control system which includes: alifting mechanism, as an example, in the form of a dual diameter piston;a pumping mechanism, as an example, in the form of a pump piston andcylinder device; and a control mechanism which includes a removable andreplaceable cartridge type directional control valve assembly whichcooperates with a secondary fluid supply system.

The cartridge type directional control valve assembly or mechanism isprovided with a novel rapid-lift load sensor or load-sensing actuatorwhich enables the platform or the forks of the pallet truck to behydraulically raised to contact a load in a single stroke of the pumphandle thereby providing for rapid-lifting and change over to a normallifting speed upon engagement of the load with the platform or forks.The hydraulic lifting unit incorporates a mechanical control forlowering the platform or forks and for operating and steering the pallettruck in a neutral mode.

Thus it is a feature of the present invention to provide a hydrauliccontrol system incorporating a lifting mechanism, a pumping mechanismand a control mechanism in the form of a cartridge type directionalcontrol valve assembly provided with a built in load-sensing actuator orsensor. With such a construction the sensor or actuator automaticallyactuates the directional control valve thus diverting the pressurizedfluid to desired port.

Another feature of the present invention is to provide a hydrauliccontrol system including a combined directional control valve assemblyand load sensor actuator which results in improved efficiency by itspositively open or closed condition allowing free flow of hydraulicfluid to desired port without restriction or flow friction.

Still another feature of the present invention is to provide a cartridgetype directional control valve assembly of the aforementioned type whichis mechanically actuated to provide other functions required in thehydraulic control system.

A further feature of the present invention is to provide a cartridgetype directional control valve which contains various ports, passagesand a series of valve elements, all arranged compactly, with the valveelements being axially aligned and actuated one by another.

A still further feature of the present invention is to provide a baseplate forming a manifold and having a manifold type bore for thereplaceable cartridge type directional control valve. In such aconstruction the base plate has the necessary hydraulic flow passagesfor the ports and passages of the control valve and further includes amechanical actuator or pressure pin for actuating the directionalcontrol valve.

Another feature of the present invention is to provide in a hydrauliccontrol system or a lifting unit a cartridge type directional controlvalve which includes as one of the valve elements a cone valve whichprovides precise flow control of the hydraulic fluid for operating andcontrolling the lowering speed of the associated pallet truck or otherlifting device.

Still another feature of the present invention is to provide in thehydraulic lift or circuit a secondary fluid supply system consisting ofpassages containing a check valve in the base plate enabling free flowof the hydraulic fluid in one direction from the reservoir to the liftcylinder during the rapid-lift stroke or operation and maintaininghydraulic pressure during the other operational modes.

A further feature of the present invention resides in the constructionof the dual diameter lifting-piston assembly and the matching dualconcentric cylinders. This positively connected dual diameter-pistonenables the lifting mechanism to operate with the hydraulic controlsystem as a highly efficient dual rate jack. This improvement eliminatesthe need for additional passages and additional control valves in themulti-function hydraulic system as utilized in the prior art.

Another feature of the present invention is to provide a pallet truckhydraulic jack having a base plate mounting an upright lift cylinder anda pump cylinder together with a frame adjustably mounted upon the baseplate and connected to the lift cylinder wherein the frame mounts aplatform or a pair of spaced horizontal forks with retractable rollersat their one ends, activation of the lift cylinder raising the frame andsimultaneously lowering the rollers relative to the forks.

Still another feature includes a manually operable pump upon a baseplate having passages formed within the base plate whereby upwardmovement of the pump piston withdraws hydraulic fluid from a reservoirthrough one such passage and into the pump cylinder and wherein manualdownward movement of the pump piston delivers pressurized hydraulicfluid to the plunger piston bore for providing a rapid lifting of anunloaded frame and connected forks with respect to a pallet.

A further feature incorporates in conjunction with a lift cylinder, adirectional control valve assembly or mechanism wherein upon the forksand frame encountering a loaded pallet for lifting thereof the controlvalve mechanism automatically responds so that pressure fluid at anincreased force is additionally delivered through an additional passagethrough the base plate to the lift cylinder to augment the lifting forceinitially provided by the plunger piston for elevating said frame andforks mounting a loaded pallet.

A still further feature incorporates into the framework retractableroller assemblies at the forward ends of the forks wherein upon powerelevation of the frame, the support rollers are lowered relative to theforks elevating the forks and the loaded pallet thereon.

Another feature includes within the hydraulic control system additionalpassages within the base plate which interconnect the reservoir and theintake to the pump so that upon the suction movement of the pump pistonhydraulic fluid is delivered from the reservoir to the pump. Uponoperation of the directional control valve located in the base plate andon downward movement of the pump piston, the connection to the reservoiris blocked, and hydraulic fluid under pressure is delivered in one ormore passages selectively to the plunger piston and to the liftcylinder.

Still another feature includes an overload valve means by which upon anoverload of the forks and frame and to protect the hydraulic jack, abypass valving is incorporated into the hydraulic control mechanismwhereby excess hydraulic fluid is returned to the reservoir.

A further feature incorporates in the hydraulic control system a rapidlift load sensor wherein with a minimum load or with the palletunloaded, there will be a fast lifting with the frame and forks orplatform with respect to the pallet upon a single activation of the pumppiston. In such a construction when the forks or platform engages theloaded pallet, the control valve mechanism is operative to overcome theload sensor and to provide for the delivery of supporting pressurizedhydraulic fluid directly to the lift cylinder which works in conjunctionwith the pressurized hydraulic fluid delivered to the plunger pistonaligned with the lift piston and rod.

A still further feature is directed to the construction of the pallettruck wherein the lift cylinder mounted upon a base plate provideslifting power to a framework with projecting forks wherein the frameworkis pivotally mounted upon the same base plate. Activation of the liftcylinder and auxiliary plunger in alignment with the lift cylindercauses lifting of the frame with respect to the base plate and at thesame time through a suitable linkage causes a lowering of the rollersrelative to the forks, in effect raising the forks relative to theground surface.

Another feature includes a manual control mechanism associated with thehandle assembly for the pallet truck and wherein the handle assemblyserves as an activating device for the pump cylinder and furthercontains a manual control assembly for the hydraulic control system suchthat in one position of the control lever, such as the lowermost "lift"position, pressurized fluid from the pump will be delivered to theplunger piston for elevating the rod within the lift cylinder for a fastlifting action with respect to an unloaded pallet and wherein when thecontrol lever is in a neutral position, the hydraulic fluid controlarrangement is such that there is a free passage of liquid back andforth between the reservoir and pump cylinder, with no movement, andwherein a further movement of the control lever to a "lowering" positionoperates the hydraulic control mechanism so as to unblock the passagesto permit the return of pressure fluid from the respective cylinders tothe reservoir for a fast lowering of the frame and forks and the loadedpallet thereon.

These and other features will be seen from the following specificationand claims in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary side perspective view of the pallet truckprovided with a hydraulic lift.

FIG. 2 is a similar view on an increased scale of the portion of thelift cylinder shown in FIG. 1 and the manual control for the pressurepin for the hydraulic directional control valve mechanism.

FIG. 3 is a fragmentary plan view on an increased scale with respect toFIG. 1 illustrating the support trunnion for the framework and thehandle pivotal mounting for the pump cylinder shown in FIG. 1.

FIG. 4 is a fragmentary side elevational view taken from the left sideof the pallet truck shown in FIG. 1 with the handle assemblyfragmentarily shown in its spring biased retracted position.

FIG. 5 is a vertical section taken through the base plate and throughthe axis of the lift and pump cylinders shown in FIG. 1, on an increasedscale illustrating a part of the hydraulic circuit.

FIG. 6 is a plan view on an increased scale, in section, taken in thedirection of arrows 6--6 of FIG. 5 and illustrating the respectivepassages forming a part of the hydraulic control mechanism or systemcorresponding to the pressure stroke of the pump for rapid lift with noload.

FIG. 7 is a partly broken away perspective view, partly in section ofthe base plate mounted lift and pump cylinders and illustrating thearrangement of the hydraulic control mechanism corresponding to pressurestroke of the pump for rapid lift with no load.

FIG. 8 is a fragmentary vertical sectional view similar to FIG. 5showing the hydraulic connections between the reservoir and the pumpcylinder on the suction stroke of the pump.

FIG. 9 is a fragmentary plan section taken in the direction of arrows9--9 of FIG. 8.

FIG. 10 is a fragmentary vertical section similar to FIG. 5,illustrating the hydraulic connections between the pump and liftcylinder corresponding to the pressure stroke of the pump with a loadapplied to the lift cylinder.

FIG. 11 is a corresponding plan section taken in the direction of arrows11--11 of FIG. 10, on an increased scale.

FIG. 12 is a fragmentary vertical section showing the hydraulicconnections between the pump and lift cylinder and plunger piston in alowering mode with hydraulic fluid under pressure returning to thereservoir.

FIG. 13 is a corresponding plan section taken in the direction of arrows13--13 of FIG. 12, on an increased scale.

FIG. 14 is a fragmentary vertical section of the hydraulic connectionswhen the control is in a neutral mode establishing fluid communicationbetween the pump and the reservoir.

FIG. 15 is a corresponding fragmentary plan section taken in thedirection of arrows 15--15 of FIG. 14.

FIG. 16 is a fragmentary vertical elevational section showing thehydraulic connections corresponding to a maximum lift condition withsome hydraulic fluid under pressure being directed back to thereservoir.

FIG. 17 is a plan section taken in the direction of arrows 17--17 ofFIG. 16, on an increased scale, showing hydraulic connectionscorresponding to the overload condition with hydraulic fluid underexcess pressure being diverted back to the reservoir.

It will be understood that the above drawings illustrate merely apreferred embodiment of the pallet truck with hydraulic lift, and thatother embodiments are contemplated within the scope of the claimshereinafter set forth.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The present invention, while relating primarily to a hydraulic liftingunit or system for a pallet truck, can also be applied to other kinds oflifting devices which include a hydraulic pump and control valve such ashydraulic service jacks, hydraulic cranes, hydraulic tables, hydraulicplatforms etc.

Referring to FIGS. 1, 2, 3 and 4 of the drawings, the present hydraulicjack or lift, generally indicated at 11 for the pallet truck of FIG. 1includes an elongated base plate 13 and depending therefrom an uprightpivot axle 15 secured to base plate 13 as by welds 17, FIG. 5. Axle 15has an elongated bore 19 and a transverse wheel assembly mount bore 21adjacent its lower end.

The upright axle support yoke 23 receives the lower end of pivot axle 15and is connected thereto by pivot pin 25 which extends through thetransverse bore 21. Accordingly, the pivot yoke 23 is adapted forpivotal movements in a vertical plane about the axis of bore 21.Transverse axle 27 extends through yoke 23 and is suitably securedthereto and mounts upon its opposite ends a pair of wheels 29, eachhaving a tire covering of polyurethane.

Transverse trunnion has a central aperture and receives pivot axle 15.Thrust bearing 33 is mounted upon the pivot axle 15 upon the top portionof the trunnion 31 and a retaining ring 35 engages the pivot axle 15below trunnion 31 for supporting the trunnion for rotary movementrelative to the pivot axle 15.

In the basic construction of the pallet truck, there is employed a pairof parallel spaced mount arms 37 at their one ends pivotally connectedat 39 to two opposite ends of the trunnion 31. The opposite ends of themount arms 37 receive the transversely extending actuator shaft 41 whichis secured to the arms 37 as by welding. The actuator shaft 41 extendsthrough lower portions of the diverging side plates of the A frame 43and adjacent its ends is rotatably mounted thereon at 45 as bestillustrated in FIG. 1.

Actuator yokes 47 are positioned within the frame 43 and secured attheir upper ends to the actuator shaft 41 and at their lower ends have adepending clevis 49 pivotally connected at 53 to the respective pushrods 51 nested longitudinally within undersurface portions of theplatform or parallel spaced forks 63. The pair of parallel spacedhorizontally disposed forks 63 at their one ends are secured as at 65 tolower portions of frame 43 and project forwardly thereof, as shown inFIG. 1.

Load rollers 59 are journaled upon yokes 57 pivotally mounted to outerend portions of the forks 63 as at 61. Upper portions of the yokes 57are pivotally connected to the ends of the push rods 51 as at 55. Theload rollers 59 in FIG. 1 are shown in a retractive position relative tothe forks 63, and upon activation of the lift or main cylinder 75, FIG.5 for elevating the frame 43 and through the linkage 37, 41, 49, 51, 55and 57, the load rollers 59 are mechanically lowered with respect to theforks 63, in effect raising the forks 63 with respect to the groundsurface S as shown in FIG. 4. Frame 43 includes at its upper end therearwardly extending frame lift cap 67 which overlies the covered swivelhead 69 upon the upper end of the lift rod 71 shown in FIG. 5.

The lift rod 71 at its lower end mounts the piston means or element 73within the hydraulic lift cylinder 75 within which it is suitably sealedfor reciprocal movement within chamber 77 therein. The upright reservoir79, adapted to contain hydraulic fluid such as oil at 89, is mountedconcentrically of the main cylinder or lift cylinder 75 upon the baseplate 13 and is secured thereto as by the welds 17.

The reservoir 79 has a fill plug 81 threaded thereinto and at its upperend mounts the piston or lift rod bearing 83 which depends within theupper end portion of the reservoir 79 and threadedly engages the upperend of the lift cylinder 75 as at 87. A suitable rod wiper 85 is nestedand retained within the lift rod bearing 83 and is adapted forcooperative sealing engagement with the reciprocal lift rod 71.

Upright pump cylinder 91 is arranged rearwardly and spaced from liftcylinder 75 and the reservoir 79 with respect to the assembly shown inFIG. 1 and is mounted upon the base plate 13 and suitably securedthereto as by the welds 17. The reciprocal pump piston 93 is movablymounted within the pump bore 99. The piston 93 mounts a pump seal 95 atits lower end. The pump piston wiper and seal 97 is nested and retainedwithin the upper end of the pump cylinder 91, surrounds and sealinglyengages reciprocal pump piston 93.

The elongated coil compression spring 101 surrounds the pump cylinder 91at its lower end bears against the base plate 13 and at its upper endmounts the spring cap 103 secured to pump piston 93 by retaining ring105. The coil spring 101 normally urges the pump piston 93 to theelevated or lift stroke suction position shown in FIG. 5.

The lower end of the pump cylinder 91 has a pump outlet 107 by whichhydraulic fluid from the reservoir 79 may enter the pump chamber 99 onsuction retraction movement of the pump piston 93 under the action ofthe coil spring 101. Upon subsequent downward compressive movementthereof pressurized hydraulic fluid will flow outwardly of the pumpoutlet 107.

A handle support 109 of bifurcated form is secured to a portion of thereservoir 79 as in FIGS. 1 and 5 and receives one end of the handlehousing 111 pivotally connected thereto by pivot bolt 117. The handleassembly including the tubular handle 113 projects down into the handlehousing 111 and is secured thereto by fastener 115, FIG. 4. Transversepressure roller 119 is mounted upon the axle 121 outwardly of andparallel to the pivot mounting 117 and is normally in registry with thepump piston 93 as shown in FIGS. 1 and 4.

The tubular handle 113 shown in FIG. 1 is adapted for manual pivotalmovement through an arc of approximately 80 degrees, by grasping theapertured grip 125 at the upper end of the handle 113 and for effectingthe downward pumping action of the pump piston 93 within the pumpcylinder 91 for delivering pressurized hydraulic fluid therefrom throughthe pump outlet 107.

There is provided upon the handle housing 111 a laterally extendingtriangularly shaped brake actuator boss 123 which is adapted when thehandle 113 has been rotated into a substantially horizontal position tooperate a suitable braking mechanism which may be applied to the truckwheels 29 should this be desired. Accordingly, in those situations whereit is desired to apply a brake to the wheels 29 of the pallet truckretaining the truck against accidental movement, a downward pivotalmovement of the handle 113 will move the brake actuator 123 into abraking device, not shown, which is adapted for frictional retainingengagement with the wheels 29 for holding the wheels 29 in a stationaryposition. This brake assembly is disclosed and claimed in Applicant'scopending United States patent application referred to at the beginningof this application.

The apertured handle grip 125 receives the upper end of the tubularhandle 113 and is suitably secured thereto as by welding. Support 127 ismounted upon the upper end of the handle 113 within the handle grip 125and supports the control lever 129 pivotally mounted upon the leversupport 127 as by the transverse pivot pin 131.

The control lever 129 has a lowermost "lift" position, an intermediate"neutral" position, and an elevated "lowering" position. An elongatedcontrol rod 133 is positioned within the tubular handle 113 and at itsupper end is pivotally connected to the control lever at 137. Lockinglever 135 is pivotally mounted upon the control lever 129 and is adaptedto operatively engage the upper end of the handle 113 when the controllever 129 has been moved to its uppermost "lowering" position.

The control rod 133 extends the length of the handle 113 and at itslower end is connected to one end of a roller link chain 141, FIG. 4which in turn at its lower end is pivotally connected to the upper endof the pull rod 139 shown in FIG. 2. Rocker pedal 143 of T shape, at oneend is connected to the lower end of the pull rod 139 by the lock nut145. The rocker pedal 143 has a depending arm 144 which extends throughand is pivotally mounted as at 149 upon the pedal support 147 suitablysecured to the lower end of the reservoir 79.

Set screw 151 is adjustably positioned upon the arm 144 and secured inposition by lock nut 152. The inner end of set screw 151 is adapted foroperative engagement with pressure pin 153 shown in FIG. 6. The pressurepin 153 is shown in the normal "lift" position to which it is biased bythe coiled spring 177 and retained with respect to the pressure pinguide 173 upon the base plate 13 by the snap ring 175.

As shown in FIG. 5, loosely within the elongated bore 19 in the pivotaxle 15 is an elongated plunger piston 155, which at its upper endprojects through base plate 13, through the plunger guide 157 and is inoperative axial engagement with the piston securing nut 159 threadedonto the lift rod 71 for securing the piston means 73 thereon.Furthermore, the plunger piston 155 is positively or mechanicallyconnected to the lift rod 71 by the solid pin 74 thereby creating orforming a dual diameter piston assembly.

The lower end of the reservoir 79, FIG. 5 has an outlet 160, sometimesreferred to as the reservoir second outlet, connected to passage 161which communicates with passage 167 within the base plate outletting at168 into the lift cylinder bore 77. The respective connected passages161 and 167 are hereafter sometimes referred to as a second passagewithin the base plate 13. Ball check valve 163 is interposed betweenpassages 161 and 167 and is normally seated by spring 165 forming a partof the ball check assembly 170.

The upper end of the bore 19 terminates in the annular inlet 169 at oneend of the passage 171, sometimes referred to as the first passagewithin base plate 13. The passage 171 at its opposite end is incommunication with the outlet 107 of the pump cylinder 91 as shown inFIG. 6.

Ball relief valve 179, FIG. 6, sometimes referred to as an overloadbypass or relief valve, is normally seated over the passage 181 in thebase plate 13 which communicates with the pump outlet 107. The reliefspring 183 normally biases the valve 179 to the position shown in FIG. 6and is adjustably secured in position by the plug 185 threaded into thebase plate 13.

At the lower end of the reservoir 79 is an outlet port 189 incommunication with passage 187, sometimes referred to as the fourthpassage, within the base plate 13, which at its other end extends to thebypass valve 179 and communicates with the passage 181, FIG. 6.

As a part of the hydraulic control mechanism or system for the presentcombination lift cylinder and lift pump, there is provided a removableand replaceable cartridge assembly 191, generally indicated in FIG. 6,which includes an elongated cartridge housing 193 which is threaded intothe transverse bore 195 within the base plate at 197. The cartridge plug199 is threaded into the outer end of the cartridge housing 193 adjacentthe bore 201 therein within which is movably mounted the change overpiston 203 having a suitable sealing O-ring thereon, there being a coilspring 205 interposed between cartridge plug 199 and one end of thechange over piston 203. The spring biased piston 203 is sometimesreferred to as a load sensor or pressure sensor. The plug 199 has a ventpassage for venting the chamber of coil spring 205.

As a part of the cartridge assembly 191, there is positioned within thecartridge housing 193, the valve retaining screw 207 which is centrallyapertured and loosely receives the shank of the cone valve 209,sometimes referred to as the first valve. The coil spring 211 is nestedwithin the valve retaining screw 207 and bears against the cone valve209 which is normally seated with respect to a central aperture withinthe cone valve insert seat 213 and which is adapted to normallyestablish communication between the first passage 171 and passage 217which is sometimes referred to as the third passage.

The steel ball 215 is a floating ball which is nested within thecartridge assembly 191 is sometimes referred to as a first valve meansor a ball check valve. Under some circumstances the ball 215 may be inthe seated position, FIG. 6 with respect to the bore 221 whichcommunicates with the bore 195 which communicates with the fourthpassage 187.

A passage 217 formed within the base plate 13 at one end is incommunication with the cylinder inlet 219 and at its opposite end is incommunication with the tapered valve 209 and the bore within which it isnested.

OPERATION Pressure Stroke-Rapid Lift-No Load

With the control lever 129, FIG. 1 in its lowermost position, being a"lift" position, the piston 93 of the pump cylinder 91 is retracted tothe lift suction position shown in FIG. 8 under the action of the coilspring 101. The previous elevation of the piston 93 creates a lowpressure condition in the chamber 99 which through the pump outlet 107and channel 171 is in communication with the reservoir outlet 189 andthe passage 187 through the transverse bore 221 shown in FIG. 9.

Under the suction created by the upward movement of the piston 93, thefloating ball 215 is unseated from the position shown in FIG. 6 to theposition of FIG. 9 to permit the flow of hydraulic fluid from thereservoir 79 through its outlet 189.

Thereafter, assuming the lift truck 11, FIG. 1 has been moved to theposition so that the respective forks 63 underlie a pallet that isloaded, the initial downward pivotal movement of the handle 113 from theposition shown in FIG. 1 80 degrees, acting through the roller 119,presses the pump piston 193 to a lowermost position.

The flow of pressurized hydraulic fluid, as shown in FIGS. 5 and 6 isthrough the pump outlet 107, through the passage 171, past the ball 215and through passage 171, FIG. 6, to the annular aperture 169 which leadsto the bore 19 thereby applying pressurized hydraulic fluid to theplunger piston 155, FIG. 5. Since the piston or lift rod 71 is thenunloaded with the forks 73 being out of engagement with the overlyingpallet, this initial action causes the plunger piston 155 to elevatefrom the position shown in FIG. 5 effecting a corresponding axial upwardmovement with the piston rod 71 and the swivel head 69. Therefore, by arapid action and a single stroke of handle 113, the piston assembly 71and 69 is moved upwardly into lifting engagement with the frame 43. Thisis referred to as a rapid lift no load pressure stroke.

As shown in FIG. 6, there is a third passage 217 within the base plate13 which is normally closed off from the first passage 171 by the springbiased seated cone valve 209 with respect to the seat 213 includingspring 211.

The cone valve 209 is furthermore yieldably seated, FIG. 6, by the loadsensor piston assembly 203 including the compression spring 205. Theload sensor 203 normally maintains the cone valve 209 in the seatedposition shown so that for the limited no load condition described, thepressure fluid from the pump cylinder 91 is delivered to only theplunger piston 155 through the first passage 171.

Since this has caused an upward movement of the piston means 73 and liftrod 71 in FIG. 5 creating a reduced pressure condition within chamber 77thereunder, some of the hydraulic fluid 89 is withdrawn from reservoir79 through the outlet 160 and through the second passage 161 and passage167 past the ball check 163 entering the lower end of the cylinder 75 at168. The withdrawn portion of hydraulic fluid 89 is then trapped inchamber 77 by the check valve 163 preventing the lift rod or cylinder 71and the connected plunger piston 155 from retracting during the nextsuction stroke of pump piston 93.

The above described functions and operation of the hydraulic jack orlift mechanism are further shown in the broken away perspective view,FIG. 7. The above described initial suction stroke is designated by thearrows in FIGS. 8 and 9. The rapid lift no load pressure stroke isdesignated by the arrows in FIGS. 5 and 6.

Pressure Stroke with Load

In order for the lift truck to elevate the loaded pallet, there is afurther pumping action of the handle 113 pressurizing the hydraulicfluid within chamber 99 of the pump, and with the loaded pallet therebycreating some resistance to the flow of pressurized hydraulic fluid inthe first passage 171, the pressure developed is sufficient to unseatthe cone valve 209 with respect to the pressure sensor 203 includingspring 205, FIG. 6. Thus, pressurized hydraulic fluid from the pumpoutlet 107 passes through the first passage 171 to activate the plungerpiston 155 providing an axial upward thrust to the piston or lift rod71. At the same time, however, additional pressurized hydraulic fluidpasses through the cartridge assembly 191 past the unseated cone valve209 and into the passage 208, and chamber 202, FIG. 11. This pressurizedhydraulic fluid activates the load sensor piston 203 retracting it fullyand disengaging it from the cone valve 209. The load sensor piston 203remains fully retracted due to back pressure from chamber 77 as long asload is applied to the lifting cylinder or rod 71. Now the first passage171 can communicate directly with the third passage 217 producing anadditional lifting force within chamber 77 acting upon the piston means73 and piston or lift rod 71 for further forcefully elevating the rod 71in conjunction with the lifting force provided by the piston plunger155. Thus, several pumping strokes of the handle 113 may be required toelevate the loaded pallet from the unloaded position of the forks shownin FIG. 1.

This arrangement and the unseating of the cone valve 209 is shownfurthermore in FIG. 11 and wherein the pressurized hydraulic fluid fromthe outlet 107 of the pump passes through both the first and thirdpassages 171 and 217 for in conjunction elevating the piston or lift rod71, and the connected piston plunger 155 in axial registry therewith aswell as the swivel head 69 which engages undersurface portions of thelift cap 67 forming a part of frame 43, FIG. 1.

This lifting action of the piston 71 and associated swivel head 69elevates the frame 43 causing a pivotal movement of the lift arms 37 ina counterclockwise direction from the position shown in FIG. 1. Theactuator shaft 41 journaled upon the framework 43 is rotating in acounterclockwise direction similarly rotating the pair of actuator yokes47. This advances longitudinally the respective push rods 51 within theforks 63. The push rods 51 at their forward ends are pivotally connectedas at 55 to the roller mounting yokes 57 rotating the yokes 57 in aclockwise direction. This effects a corresponding elevation of theloaded forks 63, so that the forks and the complete frame assemblyincluding the support wheels 29 may be moved over a support surface S tothe point of use. The arrows shown in FIGS. 10 and 11 designate thehydraulic flow during the pressure stroke with load.

Lowering

In order to lower the loaded pallet supported upon the elevated frame 43and forks 63, the control lever 129 is elevated to its uppermost"lowering" position from what is shown in FIG. 1. It is retained in thisposition by latch lever 135.

This effects an upward movement of the control rod 133 within handle 113which as shown at FIGS. 2 and 4 is connected by the chain 141 to thepull rod 139. This causes a clockwise rotation of the rocker pedal 143about the pivot mounting 149. The set screw 151 is in operativeengagement with the normally retracted pressure pin 153 which in theinitial operation is biased to the retracted position shown in FIG. 6 asby the coil spring 177.

It is this upward movement of the control lever 129 which has beencaused by the above described linkage an inward movement of the pressurepin 153 from the position shown in FIG. 6 to the position shown in FIG.13. This inward movement of the pressure pin 153 has first unseated theball 215 and at the same time the ball 215 has unseated the cone valve209. The load upon the framework 43 including the forks 63 causes thepressurized hydraulic fluid within chamber 77 of the main cylinder 75 aswell as the pressurized hydraulic fluid within the bore 19 to return bythe respective passages 171 and 217 past the cone valve 209 and past theball valve 215 returning to the reservoir 79 through passage 187 and thereservoir outlet 189. This is further shown in FIG. 12 as indicated bythe arrows. This lowering will cause a refilling of the reservoir 79with the hydraulic fluid earlier pressurized for lifting the loadedpallet.

Neutral

The control lever 129 has an intermediate "neutral" position as inFIG. 1. The linkage 143-144, 149, 151 has moved the pressure pin 153 toan intermediate position as shown in FIGS. 14 and 15. Here the ball 215has been unseated from the position shown in FIG. 6 with respect to thebore 221. However, there has not been sufficient inward movement of thepressure pin 153 as would unseat the cone valve 209, thereby maintainingpressure in chamber 77 prohibiting movement of the lifting cylinder orrod 71.

At this time, communication is established only between the pump outlet107, the corresponding first passage 171, the bore 221 with the ball 215unseated and the fourth passage 187 and the reservoir outlet 189.Accordingly, in such intermediate position, should there be any pumpingaction upon the handle 113, this would only move the hydraulic fluidback and forth between the pump chamber 99 and the reservoir 79. Otherthan that, there would be no pumping action causing any liftingmovements.

Overload

In situations where there is a considerable over load upon the pallet,in order to prevent damage to the pallet truck and/or the hydraulic jack11 provision is made as shown schematically in FIG. 17 wherein theexcess pressurized hydraulic fluid from the outlet 107 is effective tounseat the overload ball relief valve 179 FIG. 6, being normally seatedby the coil spring 183. This overload unseats the ball valve 179 andexcess pressurized hydraulic fluid is delivered through the passage 181,past the ball valve 179 and into a portion of the fourth passage 187 andthrough the outlet 189 back into the reservoir 79, such as shownadditionally in FIG. 16.

Maximum Lift

The upper end portion of the upright lift cylinder 75 is provided withthree overflow holes 230, FIG. 16, which returns excess pressurizedhydraulic fluid in lift cylinder 75 directly to the reservoir 79 asindicated by the arrows, FIG. 16. Thus when the lift rod 71 reaches itsmaximum height or lift and prior to the unseating of the relief valve179 as has already occurred in FIG. 17, the excess hydraulic fluidoverflows into the surrounding reservoir 79 as shown in FIG. 16. In sucha mode the pressure pin 153 is normally extended by the spring 177; theball valve 215 is closed by the pressure from the pump cylinder 91; thecone valve 209 is closed by back pressure in the cylinder 91; reliefvalve 179 is closed by the pressure of spring 183; check valve 163 isclosed by the differential pressure between the cylinder and reservoir(pressure in cylinder); and the change over piston 203 is moved back anddisengaged from the cone valve 209 by the pressurized hydraulic fluid inthe system.

SUMMARY

A summary of the operations and functions of the moving parts of thehydraulic lifting unit or control system is set forth in the followingtable, on the next page, with reference being made to the drawings andmodes of operation:

    __________________________________________________________________________             POSITION OF MOVING PARTS                                             MODES    PRESSURE                                                                             FLOATING                                                                             CONE    RELIEF CHECK   CHANGE OVER                     OF       PIN    VALVE  VALVE   VALVE  VALVE   PISTON                          OPERATION                                                                              (153)  (215)  (209)   (179)  (163)   (203)                           __________________________________________________________________________    SUCTION  Extended by                                                                          Opened by                                                                            Closed De-                                                                            Closed by                                                                            Closed by                                                                             Depressing cone                 STROKE   spring suction from                                                                         pressed by                                                                            spring spring  valve to closed                 (FIGS. 8 & 9)                                                                          pressure                                                                             pump   change over                                                                           pressure                                                                             pressure                                                                              position by                                            piston load            spring pressure                 PRESSURE Extended by                                                                          Closed by                                                                            Closed De-                                                                            Closed by                                                                            Opened by dif-                                                                        Depressing cone                 STROKE   spring pressure                                                                             pressed by                                                                            spring ferential                                                                             valve to closed                 RAPID-LIFT-                                                                            pressure                                                                             from pump                                                                            change over                                                                           pressure                                                                             pressure                                                                              position by                     NO LOAD                piston load    between cylin-                                                                        spring pressure                 (FIGS. 5, 6 & 7)                      der and reser-                                                                voir (vacuum                                                                  in cylinder)                            PRESSURE Extended by                                                                          Closed by                                                                            Opened by                                                                             Closed by                                                                            Closed by dif-                                                                        Moved back and                  STROKE WITH                                                                            spring pressure                                                                             pressure from                                                                         spring ferential                                                                             disengaged from                 LOAD     pressure                                                                             from pump                                                                            pump disen-                                                                           pressure                                                                             pressure bet-                                                                         cone valve by                   (FIGS. 10 & 11)        gaged from     ween cylinder                                                                         high pressure                                          change over    and reservoir                                                                         in system                                              piston         (pressure in                                                                  cylinder)                               NEUTRAL  Partially                                                                            Opened by                                                                            Closed by back                                                                        Closed by                                                                            Closed by dif-                                                                        Moved back and                  (FIGS. 14 & 15)                                                                        Depressed                                                                            pressure pin                                                                         pressure in                                                                           spring ferential                                                                             disengaged from                                        cylinder                                                                              pressure                                                                             pressure bet-                                                                         cone valve by                                                         ween cylinder                                                                         high pressure                                                         and reservoir                                                                         in system                                                             (pressure in                                                                  cylinder)                               LOWERING Fully  Opened by                                                                            Opened by                                                                             Closed by                                                                            Closed by dif-                                                                        Moved back by                   (FIGS. 12 & 13)                                                                        depressed                                                                            pressure pin                                                                         floating valve                                                                        spring ferential                                                                             pressure pin de-                                       being   pressure                                                                             pressure bet-                                                                         pressing float-                                        depressed by   ween cylinder                                                                         ing & cone valves                                      pressure pin   and reservoir                                                                 (pressure in                                                                  cylinder)                               OVERLOAD Extended by                                                                          Closed by                                                                            Closed by                                                                             Opened by                                                                            Closed by dif-                                                                        Moved back and                  (FIGS. 16 & 17)                                                                        spring pressure from                                                                        back pressure                                                                         pressure from                                                                        ferential                                                                             disengaged from                          pressure                                                                             pump   in cylinder                                                                           pump   pressure bet-                                                                         cone valve by                                                         ween cylinder                                                                         high pressure in                                                      and reservoir                                                                         system                                                                (pressure in                                                                  cylinder)                               MAXIMUM  Extended by                                                                          Closed by                                                                            Closed by                                                                             Closed by                                                                            Closed by dif-                                                                        Moved back and                  LIFT     spring pressure from                                                                        back pressure                                                                         spring ferential                                                                             disengaged from                 (FIGS. 16 & 17)                                                                        pressure                                                                             pump   in cylinder                                                                           pressure                                                                             pressure bet-                                                                         cone valve by                                                         ween cylinder                                                                         high pressure in                                                      and reservoir                                                                         system                                                                (pressure in                                                                  cylinder)                               __________________________________________________________________________

Having described my invention, reference should now be had to thefollowing claims:

I claim:
 1. In a hydraulic lifting unit having a base plate mounting anupright lift cylinder having therein a reciprocal combined lift rod andpiston means and a pump cylinder having a pump outlet and a manuallyreciprocal pump piston projecting therefrom;a hydraulic controlmechanism secured to and depending from said base plate, said controlmechanism having an elongated bore extending axially of andcommunicating with said lift cylinder; a plunger piston positionedwithin and projecting from said bore, through said base plate and at oneend secured to said lift piston means; there being a first passage insaid base plate interconnecting said pump cylinder outlet and said bore;a reservoir mounted upon said base plate containing hydraulic fluid andhaving a first outlet communicating with said first passage fordirecting hydraulic fluid into said pump cylinder upon its suctionstroke; first valve means adjacent said first passage blockingpressurized hydraulic fluid from said reservoir first outlet; downwardmovement of said pump piston directing pressurized hydraulic fluid tosaid bore thereby lifting said plunger piston and said lift cylinderpiston means and rod; said reservoir having a second outlet; there beinga second passage in said base plate at one end communicating with saidsecond outlet and at its other end communicating with said liftcylinder; upward movement of its piston means drawing hydraulic fluidfrom said reservoir into said lift cylinder.
 2. In the hydraulic liftingunit of claim 1, a normally seated valve means in said second passage.3. In the hydraulic lifting unit of claim 1, said first valve meansbeing a ball check valve in the connection between said reservoir firstoutlet and said first passage.
 4. In the hydraulic lifting unit of claim1, spring means interposed between said pump cylinder and pump pistonnormally biasing said pump piston to a retracted position;an elongatedpump handle at one end pivotally mounted upon said lift cylinder and atits other end having a grip; a pressure roller on said handle spacedfrom its pivot mounting and in registry with said pump piston, saidspring means normally maintaining said handle in an upright position,manually rotating said handle up to 80 degrees, approximately, effectingdownward movement of said pump piston compressing said spring means. 5.In the hydraulic lifting unit of claim 4, the pivot mounting of saidpump handle including a handle housing secured over said one end of saidhandle, upon one side pivoted upon said lift cylinder, said pressureroller being mounted upon the opposite side of said handle housing. 6.In the hydraulic lifting unit of claim 4, said spring means being acoiled compression spring mounted upon said base plate concentrically ofsaid pump cylinder.
 7. In the hydraulic lifting unit of claim 1, saidreservoir being concentric to said lift cylinder.
 8. In a hydrauliclifting unit having a base plate mounting an upright lift cylinderhaving therein a reciprocal combined lift rod and piston means and apump cylinder having a pump outlet and a manually reciprocal pump pistonprojecting therefrom;a hydraulic control mechanism secured to anddepending from said base plate, said control mechanism having anelongated bore extending axially of and communicating with said liftcylinder; a plunger piston positioned within and projecting from saidbore, through said base plate and at one end secured to said lift pistonmeans; there being a first passage in said base plate interconnectingsaid pump cylinder outlet and said bore; a reservoir mounted upon saidbase plate containing hydraulic fluid and having a first outletcommunicating with said first passage for directing hydraulic fluid intosaid pump cylinder upon its suction stroke; first valve means adjacentsaid first passage blocking pressurized hydraulic fliud from saidreservoir first oulet; downward movement of said pump piston directingpressurized hydraulic fluid to said bore thereby lifting said plungerpiston and said lift cylinder piston means and rod; an aperturedcartridge valve assembly within said base plate having a borecommunicating with said first passage, there being a third passage insaid base plate interconnecting said valve assembly bore and said liftcylinder; and a spring biased normally seated first valve in said latterbore closing communication between said first and third passages;increased hydraulic pressure being applied to said first passage whensaid lift cylinder piston means is loaded, unseating said first valve,pressurized hydraulic fluid feeding into said lift cylinder and applyingan increased lifting force to said piston means.
 9. In the hydrauliclifting unit of claim 8, said reservoir first outlet communicating withsaid valve assembly bore;said first valve means being a ball check valvewithin said valve assembly bore.
 10. In the hydraulic lifting unit ofclaim 8, there being a fourth passage in said base plate interconnectingsaid reservoir first outlet and said valve assembly bore;said firstvalve means being a ball check valve in said valve assembly bore forblocking pressurized hydraulic fluid from said first passage to saidfourth passage.
 11. In the hydraulic lifting unit of claim 8, thebiasing of said first valve in said valve assembly including anadjustable rapid lift load sensor changeover piston nested and sealed insaid valve assembly bore at one end axially and yieldably engaging saidfirst valve;and a coil spring within said bore engaging the other end ofsaid changeover piston.
 12. In the hydraulic lifting unit of claim 10,said fourth passage extending to said pump cylinder outlet;and anormally closed overload bypass valve in said fourth passage; maximumpressurized hydraulic fluid when applied to said first and thirdpassages to said lift cylinder opening said bypass valve for fluidcommunication to said fourth passage and to said reservoir.
 13. In thehydraulic lifting unit of claim 10, said upward movement of said pumppiston drawing hydraulic fluid through said fourth passage, past saidball check valve and into said first passage.
 14. In the hydrauliclifting unit of claim 10, a normally retracted spring biased pressurepin in said base plate coaxial to and normally spaced from said ballcheck valve;manual inward movement of said pressure pin moving said ballcheck valve into engagement and unseating said first valve within saidvalve assembly; the load acting on said lift cylinder piston meansreturning hydraulic fluid from said bore and lift cylinder through saidfirst and third passages past said first valve and ball check valvethrough said fourth passage and into said reservoir.
 15. In thehydraulic lifting unit of claim 14, said pressure pin having a "neutral"position intermediate its "retracted" and "advanced" position whereinsaid ball check valve is unseated establishing communication betweensaid fourth passage to said reservoir and said first passage to saidpump cylinder, said first valve remaining seated.
 16. In the hydrauliclifting unit of claim 11 wherein said cartridge valve assembly includingsaid load sensor changeover piston is threadedly mounted as a unit insaid base plate and may be removed and replaced when required.
 17. In ahydraulic lifting unit having a base plate mounting an upright liftcylinder having therein a reciprocal combined lift rod and piston meansand a pump cylinder having a pump outlet and a manually reciprocal pumppiston projecting therefrom;a hydraulic control mechanism secured to anddepending from said base plate, said control mechanism having anelongated bore extending axially of and communicating with said liftcylinder; a plunger piston positioned within and projecting from saidbore, through said base plate and at one end secured to said lift pistonmeans; there being a first passage in said base plate interconnectingsaid pump cylinder outlet and said bore; a reservoir mounted upon saidbase plate containing hydraulic fluid and having a first outletcommunicating with said first passage for directing hydraulic fluid intosaid pump cylinder upon its suction stroke; first valve means adjacentsaid first passage blocking pressurized hydraulic fluid from saidreservoir first outlet; downward movement of said pump piston directingpressurized hydraulic fluid to said bore thereby lifting said plungerpiston and said lift cylinder piston means and rod; an elongated tubularpump handle pivotally mounted upon said base plate operably engageablewith said pump piston and having a grip, said handle projecting intosaid grip; a control lever within said grip projected into and pivotallymounted upon said handle; said control lever having a lower "lift"position, an intermediate "neutral" position, and an upper "lowering"position; an aperture cartridge valve assembly within said base platehaving a bore communicating with said first passage, there being a thirdpassage in said base plate interconnecting said valve assembly bore andsaid lift cylinder; a spring biased normally seated first valve in saidlatter bore closing communication between said first and third passages;increased hydraulic pressure being applied to said first passage whensaid lift cylinder piston means is loaded, unseating said first valve,pressurized hydraulic fliud feeding into said lift cylinder and applyingan increased lifting force to said lift piston means; there being afourth passage in said base plate interconnecting said reservoir firstoutlet and said valve assembly bore; said first valve means being a ballcheck valve in said valve assembly bore for blocking pressurizedhydraulic fluid from said first passage to said fourth passage; anormally retracted spring biased pressure pin in said base plate coaxialto and normally spaced from said ball check valve; manual inwardmovement of said pressure pin moving said ball check valve intoengagement with and useating said first valve within said valveassembly; the load acting on said lift cylinder piston returninghydraulic fluid from said bore and lift cylinder through said first andthird passages past said first valve and ball check valve through saidfourth passage and into said reservoir; and a linkage meansinterconnecting said control lever and said pressure pin, and includinga control rod nested within said handle at one end pivotally connectedto said control lever; said pressure pin being retracted with thecontrol lever in a lift position, said pressure pin being in a neutralintermediate position when said control lever is in a neutral position;said pressure pin being in an advanced position to unseat said firstvalve when the control lever is in a lowering position.
 18. In thehydraulic lifting unit of claim 17, said linkage means further includinga rocker pedal pivotally mounted upon said lift cylinder and engagingsaid pressure pin;and a flexible linkage between the lower end of saidcontrol and said rocker pedal whereby upward pivotal movement of saidcontrol lever advances said pressure pin inwardly.
 19. In the hydrauliclifting unit of claim 17, a locking lever pivotally mounted upon saidcontrol lever and engageable with said handle when said control lever ispivoted to its uppermost "lowering" position.